[texodus]

This PR adds setCommandSchema(), an API which lets an app embedding <perspective-viewer> add its own commands to the right-click menu, with click context.

viewer.setCommandSchema((context) => {
      const id = context.hit?.row.security_id;
      return {
            commands: id == null ? [] : [{
                  kind: "Command",
                  key: "open-ticket",
                  label: `Open Ticket (${id})`,
            }],
      };
});

viewer.addEventListener("perspective-command", (event) => {
      const { key, context } = event.detail;
      if (key === "open-ticket") {
            openOrderTicket(context.hit.row.security_id, context.point);
      }
});

• setCommandSchema() takes a synchronous function from a context (panel, table, plugin, view config, click point, and the hit under the cursor) to a list of Command / Group entries, shaped like plugin_config_schema.
• Picking a command fires perspective-command with its key and the same context.
• Plugins gain three optional methods: hit_test(x, y), plus command_schema() / execute_command() to offer commands of their own. Datagrid and charts implement hit_test.
• React: commandSchema and onCommand props.
• With no schema set, the right-click path is unchanged.